Why are genes from one parent expressed and the other parent not: new ideas on genomic imprinting

The question of how we reach a situation where a gene is expressed from a certain parent and not from the other parent, is now better understood with the help of research on the duck and the wallaby - and it seems that this did not arise in a way related to the sex chromosomes

The question of how we reach a situation where a gene is expressed from a certain parent and not from the other parent, is now better understood with the help of research on the duck and the wallaby - and it seems that this does not arise in a way related to the chromosomes of the species.

A new study published in the online magazine 'BMC evolutionary biology' contributed little to the understanding of the evolution of genomic imprinting, a phenomenon in which genes from chromosomes received from a certain parent are expressed, while the same genes on the chromosome received from the other parent are inhibited.

Imprinting results from a kind of epigenetic memory - modifications on the DNA from a certain parent, such as through the packaging of the genetic material in the chromosome, which prevent the genes in it from being expressed. The reasons for the development of imprinting are not understood. It is known, however, that different patterns of imprinting appear in different types of mammals, with some types exhibiting the phenomenon and others not. Since the evolutionary relationships between mammals are well documented, the imprinting patterns in the different genomes can be important clues in understanding the evolution of imprinting.

One theory is that imprinted genes came from the sex chromosomes, which could be epigenetically 'silenced' for the purpose of regulating genetic dosage between partners. Another idea is that the imprinting arose from a common parent chromosome that itself was imprinted.

A research group led by father and daughter, Malcolm and Ann Ferguson-Smith from the University of Cambridge, tested these ideas by mapping known sequences of imprinted genes in two species; The monotreme platypus and the marsupial wallaby. These species represent recognized positions in the evolution of mammals.

The results of the study show that imprinted genes were not located like this on a common parent chromosome nor on the sex chromosomes. It seems that the imprinting developed in stages, according to need when each gene or group of genes underwent imprinting when the need arose.

This study is important not only for its evolutionary findings, but also because the duck is a relatively uncharacterized species. By finding the relationship between specific sequences and certain chromosomes, the researchers located important genetic markers in the duck genome.
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